Photographic process



Patented Oct. .17, 1939 TUNiTED STATES PATENT OFFlCE v T rnorooifs r zr z raooass t William Henry Evans, Huntington Park, Calif.

No Drawing. Application July 15, 1938, Serial No. 219,408

. 1o (CI. 95-88) This invention relates to the production of colored photographic images either for-viewing by transmitted or reflected light, and has for its object the provision of a method which will give 5 colored photographs with greater accuracy, certainty and ease than provided by processes heretofore known and used.

Briefly the process consists in the transforming of the usual silver deposit which forms the black and white image in a photographic emulsion coating into a latent image, which is capable of being converted into a colored dye image by treatment in suitable acid dye solutions in the presence of.

certain dye activators. Positives from color separation negatives may thus be changed to color transparencies and superimposed to form natural color photographs or. transparencies, or the stained images may-be transferred, one color at a time, to other emulsion surfaces such.as gelatine,

by an imbibition process to produce colored prints; subsequently the latent image maybe repeatedly stained and transferred to other fresh emulsion surfaces. The latent images'may also be stained, and the first stainQdifierentiaily replaced by a different dye, giving a twoor. multiple-toned effect. j

The process will be described asapplied to-the preparation of a superimposed colored image photograph made-from three-color separation nega- 'tives. Full rich positive prints in black and white of the color-separation negatives are first made, preferably on strip film. The positives on strip film are developed to give full detail,

'and are then put into an acid-stop bath, followed 85 bywashing in water. The silver image is then removed and a latent image, barely visible by reflected light, is produced in its place by the use A of a special bleaching reagent. Inits' preferred 7 composition, this bleaching reagent consists of 20 40 grams copper sulphate, 10 grams potassium bromide, and two grams chromic acid in one liter of water. chromicacid, may be used as described below.

After the silver has been removed, the film is 45 washed and treated in an acid "hypo fixing bath (without hardener). T he hypo solution is then removed by washing, and the latent image in the gelatine may be dyed immediately, or the emulsion and backing may be allowed to dry, and v tion of'an acid dye in the presence of an activating agent such assodium acetate. I prefer to use a Other compositions, all containing free may be'varied to suit conditions and strength of color required. 'In the presence of the activator, and with a latent image formed in-gelatine by the procedure and with the reagents as described,

the coloring by the dye takes place substantially wholly in the portions where the silver image originally existed, and substantially not atall in the highlights. If strip film has been used, the gelatine layer and the thin cellulose backing is 1 stripped from the thicker supporting film, and the dyed image is then washed with water to remove adhering dye, or to remove excess if the image has become too deep in color.

- The color is fixed by washing the film in a one- 20 percent acetic acid bath. The red, blue and yellow colored images corresponding to the threecolor separation positives are then squeegeed in register on a gelatine coated backing such as paper, celluloid or transparent nitrocellulose or as the like. i

Instead of superimposing the three dyed gelatine strip'films to form a color composite, each of these may be used as a matrix to carry colorto a gelatine coated backi by an imbibition proc- 3oess. In this alternative, after dyeing the latent images as above described, the dyed gelatine surface is placed in contact with a 'gelatine coated bficlsh ig sheet which has been previously soaked in releasing" reagent, preferably about one-' half percent sodium sulphite in water. The other colors are transferred to the gelatine coated backing in register with the previously imbibed image in the same manner, resultingfinally in a three color print, which is fixed in dilute acetic acid Y (about one percent) and dried. The dyed films may then be washed and redyed and the dye. transferred by imbibition to other prints as'before.

One, two or multiple color prints and transparencies may be made by variations of my process.

Single or. multiple color effects may be produced by applying my process to ordinary "black and white positives made from negatives taken so on the usual photographic emulsions. The silver image is removed and the latent image produced by treatment with the chromic acid solution as above, following which the latent image is dyed in a desired background color using acid dyes in g Instead of using a .positive print from duced to one-fourth of the above amount that the presence of an activator such as sodium acetate. Then, by treating the dyed image in an other color acid dye bath containing activator, the second dye replaces the first in the lighter tones, the shadows remaining predominately of the first color. By stopping the process of replacement at any desired time, novel two-toned elects, or multiple color effects may be easily produced from an ordinary non-separation negative or print.

Instead of immersing the print in the second color bath, the second, and subsequent colors may 'be manually applied locally as desired to give the desired color replacements.-

original exposed and developed negative, the neg ative itself may be used by employing any wellknown "reversaP process .to form what isin efdye 'in'the presence of the activator, in the same f manner as above described fora positive.

The preferred reagent for producing the latent image and removal of the silver image has been given above as 20 parts copper sulphate, 10 parts potassium bromide, and 2 parts chromic acidin 1000 parts water. The ratio of chromic acid to copper sulphate is important, it having been found that if the quantity of chromic acid be re- Other sulphates such as potassium or sodium sulphates may be used but these do not give nearly as good results as copper sulphate.

After the silver has been removed and the latent image produced as above described, the dye is absorbed selectively in the latent image portion and not in theother portions, when an activator is used with an acid dye, the dye being in quite dilute solution. Acid dyes are desirable in' color photography because they are not dichroic and because the colors are such that natural color effects may be formed by their superimposition for both reflected and transmitted light. The dye activator which I have found to give the best results is sodium acetate in dilute solution, onehalf to two grams per liter of dye solution in water being preferred. vAn increase in the sodium acetate concentration causes more and more staining in the highlights and less and less staining in the shadows, with the necessity of washin back, which has the effect of reducing the shadows andincreasing the highlights. The dye solution used is dilute, being preferably from about have been colored by staining the whole gelatine film, and then attempting to' selectively wash out the dye from the highlights. This requires: that some coloring shall remain in the image when the washing is continued to the point where clear portions were free from dye. The result was a weak colored image, with much detail lost in the process. By my process the latent image alone takes up the dye when the activator is present, and the clear .portions remain substantially undyed except for adhering surface solution which is quickly and easily rinsed oil. It is essential that the latent-gelatine image be produced with relatively dilute chromic acid reagent in the presence of copper sulphate, in order that the activating agent usedwith the'dye will causeselec tive dyeing of the image. Bleached silver images using any previously known "bleaching agents are not differentially dyed to any, practical extent in the presence of my activator in the dye solution.

The temperatures used throughout my process, including the formation of the latent gelatine image and the activator-dyeing process are the normal photographic operative temperatures, usually not in excess of about 85 degrees'F. The effect of temperature increases, so far as I have observed, is merelyto increase the speed of the reactions.

type of photographic silver emulsions in gelatine may be employed in my process, and the gelatine coating may be unhardened, partially hardened, or hardened such as in litho-type film. I have found that the selective dyeing by my process is effective regardless of the previous hardening of the gelatine coating by any of the well.

known hardening methods now employed in photographic practice.

While I have illustratedmy process with several variations by specificiexamples and preferred reagents, I do not wish to thereby limit the scope of my invention, except insofar as may be re quired by the prior art and the spirit of the appended claims.

I claim:

1. The process of coloring a photographic image comprising developing a light exposed silver halide type photographic emulsion, treating it without fixing in a bath which simultaneously removes the reduced silver image and forms a latent non-silver image capable of becoming a 1 from said emulsion by treating in a fixing bath,

and then staining said latent image with a solution containing sodium acetate and an acid dye of the type which is non-dyeing'to gelatin in the presence of an' alkali.

2. The process of coloring a photographic image comprising dev loping a light-exposed silver halide type photographic emulsion, treating it in a bath containing dilute chromic acid which simultaneously removes the reduced silver image and forms a latent non-silver image capable of becoming a color image when treated with acidtype dyes in the presence-of an activator for said dyes, removing the silver salts from said emulsion by treating in a fixing bath, and staining said non-silver image with an acid-type dye solution containing sodium acetate.

3. The process of coloring a photographic image comprising developing a light-exposed silver halide type photographic emulsion, treating it in a bath containing dilute chromic acid and a copper salt which simultaneously removes the reduced silver image and forms a latent nonsilver. image capable of becoming a color image when treated with acid-type dyes in the presence of an activator for said dyes, removing the silver salts from said emulsion by treating in a fixing bath, and staining said non-silver image with an acid-type dye solution containing sodium acetate.

4. The process of coloring a photographic image comprising developing a'light-exposed silver halide type photographic emulsion, treating it in a bath containing from 1 to 6 parts chromic acid with 20 parts copper sulfate and about parts potassipm bromide in 1000 parts of water which simultaneously removes the reduced silver image and forms a latent non-silver image capable of becoming a color. image when treated with acid-typedyes in the presence of an activator for said dyes, removing the silver salts from said emulsion by treating in a fixing solution, and staining said non-silver image with an acidtype dye solution containing sodium acetate.

5. In the process of coloring a latent nonsilver chromic acid bleached image in a photographic emulsion comprising the step of staining said latent image by treatment in a water solution of an acid dye in the presence of sodium acetate. I

6. In the process of -coloring a latent nonsilver chromic acid bleached image in a photographic emulsion comprising the steps of stainimmersing the sheet in an aqueous acid-type dye solution in thepresence of sodium acetate.

8. The process of forming a colored photographic image comprising treating a light exposed developed silver image in a photographic emulsion sheet with a bath containing dilute chromic acid and copper sulphate to form a latent image area on said sheet, and staining said latent image area by immersing the sheet in an aqueous acid-type 'dye solution in th presence of sodium acetate. 9. The process of coloring a photographic .image comprising developing a light-exposed silver halide type photographic emulsion, treating it in a bath containing from 1 to 6 parts chromic acid with 20 parts copper sulfate and about 10 parts potassium bromide in 1000 parts of water which simultaneously removes the reduced silver image and forms a latent non-silver image capable of becoming a.color image when treated with acid-type dyes inthe presence of an activator for said dyes, removing the silver salts from said emulsion by treating in a fixing solution, and staining said non-silver image with a solution containing about one part acid-type dye and one part sodium acetate in 1000 parts of water. 7 10.- The process of making a multicolored photographic print comprising forming colorseparation silver images, in separate photographic emulsions, treating the formed silver images with a bleaching solution containing chromic acid but free from dichromates thereby removing the silver image and forming latent non-silver images in each of said emulsions,

separately staining each of said latent images bytreatment in a dilute water solution of an appropriately coloredacid dye in the presence of sodium acetate, and superimposing. in register the colored images in; the separate emulsions.

WILLIAM HENRY EVANS. 

